无法将设置转换为地图[关闭]

Question

我正在尝试创建字符串及其长度的映射。key是长度，value是string。

public class Task2 {
    public static void main(String[] args) {

        final var strings = new HashSet<>(Arrays.asList("one", null, "three", null, "five"));

        System.out.println("Filter HashSet: ");

        Map<String, String> result = strings.stream()
                .filter(Objects::nonNull)
                .map(String::length)
                .collect(Collectors.toMap();
        
    }
}

Answer 1

如果您想获取键是字符串“一”、“三”、“五”并且值是相应字符串的长度的映射，那么您可以使用

        Map<String, String> result = strings.stream()
                .filter(Objects::nonNull)             
                .collect(Collectors.toMap(k->k, String::length));

Answer 2

final var strings = new HashSet<>(Arrays.asList("one", null, "three", null, "five",null,"six"));
    
System.out.println("Filter HashSet: ");   
Map<Object, List<String>> result = strings.stream()
                    .filter(Objects::nonNull)
                    .collect(Collectors.groupingBy(x->x.length()));
 System.out.println(result);

输出：

Filter HashSet: 
{3=[six, one], 4=[five], 5=[three]}

Answer 3

这里的键是字符串的长度，值是字符串本身

Map至少需要两个参数。关键和价值。如果需要长度和字符串，则map键必须是整数类型。第三个参数是一个合并函数，以防字符串长度相同。它只是附加它们，用逗号分隔。

final var strings = new HashSet<>(
        Arrays.asList("one", null, "three", null, "five", "six", "four"));

System.out.println("Filter HashSet: ");

Map<Integer, String> result =
        strings.stream().filter(Objects::nonNull).collect(
                Collectors.toMap(a -> a.length(), a->a, (a,b)->a + ", " + b));

result.entrySet().forEach(System.out::println);

指纹

Filter HashSet: 
3=six, one
4=four, five
5=three